Fix potential out-of-bounds access by checking if start is empty before removing prefix

[flylai]

If the code contains compiler builtin functions, it will crash with /usr/include/c++/14.2.1/string_view:297: constexpr void std::basic_string_view<_CharT, _Traits>::remove_prefix(size_type) [with _CharT = char; _Traits = std::char_traits<char>; size_type = long unsigned int]: Assertion 'this->_M_len >= __n' failed.

In other words: "support compiler builtin functions"

eg:

#include <inttypes.h>

/* WARNING: undefined if a = 0 */
static inline int clz32(unsigned int a)
{
    return __builtin_clz(a);
}

/* WARNING: undefined if a = 0 */
static inline int clz64(uint64_t a)
{
    return __builtin_clzll(a);
}

/* WARNING: undefined if a = 0 */
static inline int ctz32(unsigned int a)
{
    return __builtin_ctz(a);
}

/* WARNING: undefined if a = 0 */
static inline int ctz64(uint64_t a)
{
    return __builtin_ctzll(a);
}

after fixes, the result is:

#include <inttypes.h>

static inline int clz32(unsigned int a)
{
  return __builtin_clz(a);
}

 __attribute__((nothrow)) __attribute__((const)) extern int __builtin_clz(unsigned int);

static inline int clz64(uint64_t a)
{
  return __builtin_clzll(static_cast<unsigned long long>(a));
}

 __attribute__((nothrow)) __attribute__((const)) extern int __builtin_clzll(unsigned long long);

static inline int ctz32(unsigned int a)
{
  return __builtin_ctz(a);
}

 __attribute__((nothrow)) __attribute__((const)) extern int __builtin_ctz(unsigned int);

static inline int ctz64(uint64_t a)
{
  return __builtin_ctzll(static_cast<unsigned long long>(a));
}

 __attribute__((nothrow)) __attribute__((const)) extern int __builtin_ctzll(unsigned long long);

[andreasfertig]

Hello @flylai,

thanks for the PR!

Could you please also add a test for this change? You find them under tests. Since this is also a fix you can use the notation Issue681.cpp and Issue681.expect. Copy your initially failing code into the .cpp and the working output of C++ Insights into .expect. Thank you!

Andreas

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.85%. Comparing base (a84a979) to head (8d29d87).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #681   +/-   ##
=======================================
  Coverage   97.85%   97.85%           
=======================================
  Files          20       20           
  Lines        6534     6535    +1     
=======================================
+ Hits         6394     6395    +1     
  Misses        140      140           

Flag	Coverage Δ
insights-macos	97.13% <100.00%> (+<0.01%)	⬆️
insights-ubuntu-amd64-libcxx-No	98.10% <100.00%> (+<0.01%)	⬆️
insights-ubuntu-amd64-libcxx-Yes	98.08% <100.00%> (+<0.01%)	⬆️
insights-ubuntu-arm64-libcxx-No	98.06% <100.00%> (+<0.01%)	⬆️
insights-ubuntu-arm64-libcxx-Yes	98.04% <100.00%> (+<0.01%)	⬆️

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[flylai]

Hi @andreasfertig
Test case have been added to commit.

[andreasfertig]

Hello @flylai,

thanks for the test! Unfortunately, it failed. I suspect for the output you posted you had other C++ Insights options enabled?
While you can teach the test this, I think its best to had the plain transformation tested. Could you please adjust the test result?

Andreas

[flylai]

Hi @andreasfertig
I am using Archlinux with clang 18.1.8, and I retry the tests with build arguments as follows

cd cppinsights
mkdir build
cd build
cmake .. -DINSIGHTS_USE_SYSTEM_INCLUDES=off -DCLANG_LINK_CLANG_DYLIB=on -DLLVM_LINK_LLVM_DYLIB=on -DCMAKE_CXX_COMPILER=clang++
make tests -j24

and the cmake output:

-- The CXX compiler identification is Clang 18.1.8
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/clang++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- llvm_config(LLVM_CXXFLAGS)=>-I/usr/include    -fno-exceptions -funwind-tables -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS;
-- llvm_config(LLVM_LDFLAGS)=>-L/usr/lib;
-- llvm_config(LLVM_LIBS2)=>-lLLVM-18;
-- llvm_config(LLVM_LIBDIR)=>/usr/lib;
-- llvm_config(LLVM_INCLUDE_DIR)=>/usr/include;
-- llvm_config(LLVM_SYSTEM_LIBS2)=>;
-- llvm_config(LLVM_PACKAGE_VERSION)=>18.1.8;
-- Generating version.h
-- Found clang-tidy: /usr/bin/clang-tidy
-- Could not find the program include-what-you-use
-- Found Doxygen: /usr/bin/doxygen (found version "1.13.1") found components: doxygen dot
-- Found Python3: /home/lkm/pyvenv/bin/python3.13 (found version "3.13.1") found components: Interpreter
-- Found Python3: /home/lkm/pyvenv/bin/python3.13. Target tests enabled.
-- 
-- [ Build summary ]
-- BUILD_INSIGHTS_OUTSIDE_LLVM : On
-- CMAKE_GENERATOR       : Unix Makefiles
-- CMAKE_EXE_LINKER_FLAGS: 
-- CMAKE_LINKER          : /usr/bin/ld
-- CMAKE_OSX_ARCHITECTURES : 
-- Compiler ID           : Clang
-- Compiler version      : 18.1.8
-- Compiler path         : /usr/bin/clang++
-- llvm-config           : /usr/bin/llvm-config
-- Min LLVM major version: 18
-- Install path          : /usr/local
-- Clang resource dir    : 
-- CMAKE_SOURCE_DIR      : /home/lkm/dev/cppinsights
-- CMAKE_BINARY_DIR      : /home/lkm/dev/cppinsights/build
-- Git repo url          : https://github.com/andreasfertig/cppinsights.git
-- Git commit hash       : 59bd291cf159e28ccbb955c977edb72dc18fd02b
-- Debug                 : OFF
-- Code Coverage         : OFF
-- Static linking        : OFF
-- Strip executable      : ON
-- Elevate includes:     : off
-- clang-tidy            : Off
-- include-what-you-use  : Off
-- 
-- Configuring done (0.3s)
-- Generating done (0.0s)
-- Build files have been written to: /home/lkm/dev/cppinsights/build

and the latest output is

#include <inttypes.h>

static inline int clz32(unsigned int a)
{
  return __builtin_clz(a);
}

static inline int clz64(uint64_t a)
{
  return __builtin_clzll(static_cast<unsigned long long>(a));
}

static inline int ctz32(unsigned int a)
{
  return __builtin_ctz(a);
}

static inline int ctz64(uint64_t a)
{
  return __builtin_ctzll(static_cast<unsigned long long>(a));
}

It is still different with the macOS test result, I will adjust the test result.